Bulletin of the Mizunami Fossil Museum, no. 44 (2018), p. 59–67, 2 figs. © 2018, Mizunami Fossil Museum Five new species of the genus Semisulcospira (Mollusca: Caenogastropoda: Semisulcospiridae) from the Pleistocene Katata Formation of the Kobiwako Group, Shiga Prefecture, central Japan Keiji Matsuoka* and Osamu Miura** *Toyohashi Museum of Natural History, 1-238 Oana, Oiwa-cho, Toyohashi, Aichi 441-3147, Japan <
[email protected]> **Faculty of Agriculture and Marine Science, Kochi University, 200 Monobe, Nankoku, Kochi 783-8502, Japan <
[email protected]> Abstract Five new species of the freshwater snail genus Semisulcospira are described from the Pleistocene Katata Formation of the Kobiwako Group in central Japan. Semisulcospira contains two subgenera, Semisulcospira and Biwamelania, and these five new species belong to the subgenus Biwamelania. Semisulcospira (Biwamelania) nakamurai nov. sp., Semisulcospira (Biwamelania) pseudomultigranosa nov. sp., Semisulcospira (Biwamelania) spinulifera nov. sp., Semisulcospira (Biwamelania) kokubuensis nov. sp., and Semisulcospira (Biwamelania) pusilla nov. sp. are described herein. These species appear to be the direct ancestors of fifteen extant species of Biwamelania that have been diversified in Lake Biwa for the last approximately 400,000 years; then, these occurrences can provide valuable information to understand the history of diversification of Biwamelania species in Lake Biwa. Key words: Freshwater snail, Mollusca, Semisulcospiridae, Semisulcospira, Biwamelania, Kobiwako Group, Pleistocene, Lake Biwa, Japan Introduction Biwamelania (Watanabe and Nishino, 1995; Nishino and Watanabe, 2000). While the subgenus Biwamelania is The genus Semisulcospira Boettger, 1886 is widely currently endemic to Lake Biwa and its drainage, the fossil distributed and one of the most abundant molluscs in species of Biwamelania has a broader distribution range in freshwater environments of East Asia (Davis, 1969; Burch Tokai, Kinki, and Kyushu regions during the Pliocene and et al., 1987; Strong and Köhler, 2009).